EP0072306B1 - Method of preparing a composite material comprising an inorganic matrix in which vitreous carbon inclusions are dispersed, material obtained by this process and its utilisation as an electric contact - Google Patents

Method of preparing a composite material comprising an inorganic matrix in which vitreous carbon inclusions are dispersed, material obtained by this process and its utilisation as an electric contact Download PDF

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EP0072306B1
EP0072306B1 EP82401443A EP82401443A EP0072306B1 EP 0072306 B1 EP0072306 B1 EP 0072306B1 EP 82401443 A EP82401443 A EP 82401443A EP 82401443 A EP82401443 A EP 82401443A EP 0072306 B1 EP0072306 B1 EP 0072306B1
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EP
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Prior art keywords
inclusions
resin
process according
heat treatment
vitreous carbon
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EP82401443A
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German (de)
French (fr)
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EP0072306A1 (en
Inventor
Jacques Devillard
Jean Granier
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Commissariat a lEnergie Atomique et aux Energies Alternatives CEA
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Commissariat a lEnergie Atomique CEA
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    • C—CHEMISTRY; METALLURGY
    • C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
    • C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
    • C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
    • C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
    • C04B35/52—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite
    • C04B35/524—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbon, e.g. graphite obtained from polymer precursors, e.g. glass-like carbon material
    • C—CHEMISTRY; METALLURGY
    • C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
    • C22C—ALLOYS
    • C22C32/00—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ
    • C22C32/0084—Non-ferrous alloys containing at least 5% by weight but less than 50% by weight of oxides, carbides, borides, nitrides, silicides or other metal compounds, e.g. oxynitrides, sulfides, whether added as such or formed in situ carbon or graphite as the main non-metallic constituent
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material
    • H01H1/025—Composite material having copper as the basic material
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
    • H01H1/00—Contacts
    • H01H1/02—Contacts characterised by the material thereof
    • H01H1/021—Composite material
    • H01H1/027—Composite material containing carbon particles or fibres

Definitions

  • the present invention relates to composite materials comprising an inorganic matrix in which are included inclusions of carbonaceous material, constituted by inclusions of vitreous carbon and / or graphite and / or carbides.
  • Such composite materials can be used in many fields, in particular in the electrical engineering and mechanical industry as electrical contact materials and / or friction materials.
  • the invention relates to a process for preparing composite materials comprising vitreous carbon inclusions of controlled dimensions, distributed in a substantially uniform and regular manner within a dense or porous inorganic matrix, preferably metallic.
  • vitreous carbon is an artificial variety of carbon which is obtained by pyrolysis, under rigorously controlled conditions, of crosslinked polymers obtained by polycondensation of phenols and aldehydes.
  • the carbon obtained during this pyrolysis is called vitreous carbon because of its appearance, its hardness, its brittleness (comparable to that of porcelain), and its impermeability to gases which are comparable to those of glass.
  • the pyrolysis of the crosslinked polymer is carried out in such a way that the three-dimensional network of the polymer is preserved during the operation and gives the final product this particular structure.
  • Vitreous carbon has interesting properties for various applications. Indeed, given its particular structure which delimits micropores which do not communicate with each other and do not open onto the surface of the material, the latter has a low density of the order of 1.45 whereas that of graphite is 2.2. Furthermore, its mechanical properties are close to those of pyrolithic graphite or pyrocarbon; and its thermal properties: a thermal conductivity of the order of 0.04 to 0.08 Joule / cm -1 ⁇ ° C -1 ⁇ S -1 and a coefficient of expansion of the order of 3 to 5 ⁇ 10 6 ⁇ ° C -1 to 100 ° C and from 20 ⁇ 10 -6 ⁇ ° C -1 to 1500 ° C, give it remarkable resistance to thermal shock. In addition, vitreous carbon has a higher resistance to oxidation than that of other varieties of carbon and graphite, in particular a good resistance to oxidation by oxygen, water vapor or carbon dioxide.
  • the present invention specifically relates to a process for preparing a composite material comprising inclusions of carbonaceous materials, in particular vitreous carbon, which makes it possible to obtain a uniform and regular dispersion of these inclusions within a porous inorganic matrix. or compact while controlling the maximum dimension of these inclusions as well as the content of carbonaceous material in the product obtained.
  • the process of the invention makes it possible to carry out effectively and economically the control of the composition of the product independently of the control of the size of the inclusions.
  • the mixture of resin and inorganic powder is subjected to a shaping operation by cold compression, in order to obtain a preform.
  • This compression operation can be carried out by pressing, spinning, rolling or extruding so as to put the dough in the form of sheets, cylinders, etc., but it is preferably carried out under conditions such as the dough does not become compact to allow the evacuation of gases during subsequent heat treatments.
  • the heat treatments can be carried out on a compact paste.
  • the inorganic powder used is a sinterable powder, that is to say of an inorganic material capable of being shaped and consolidated by the techniques of powder metallurgy; moreover, this inorganic material is chosen so that it is not fusible at the temperatures used for the first and second heat treatments.
  • Mention may be made, as inorganic materials which can be used, of metals such as copper and nickel; alloys, ceramics such as oxides, carbides and nitrides, for example boron nitride, and cermets. It is also possible to use coated powders or mixtures of powders of different materials, for example, materials capable of reacting with each other under the processing conditions to form a liquid phase.
  • the particle size of the inorganic powder used is chosen according to the dimension of inclusions which it is desired to obtain. Generally, a powder is used whose average particle size is between 0 and 600 ⁇ m.
  • the resin used is advantageously a liquid resin, comprising phenolic radicals (such as phenol, resorcinol, naphthalene diol, etc.) and radicals derived from aldehydes (such as formaldehyde, glyoxal, furfuraldehyde, etc.).
  • phenolic radicals such as phenol, resorcinol, naphthalene diol, etc.
  • aldehydes such as formaldehyde, glyoxal, furfuraldehyde, etc.
  • the liquid resin is a phenol formaldehyde resin.
  • the mixture of resin and inorganic powder contains at most 20% by weight of resin.
  • the first heat treatment is advantageously carried out at a temperature at most equal to 350 ° C. for a period of 1 to 3 hours.
  • this first heat treatment polycondensation of the resin is obtained, which leads to the formation of a solid crosslinked polymer and to the obtaining of a cured product.
  • the gases released during this reaction can be evacuated, which makes it possible to avoid the appearance of significant porosity and / or the formation of cracks in the cured product.
  • This hardened product is then subjected to a second heat treatment to transform the solid polymer into vitreous carbon. This second treatment must be carried out under rigorously controlled conditions so as to preserve the three-dimensional network of the crosslinked solid polymer.
  • this second treatment is carried out under vacuum or under a neutral atmosphere at a temperature of 600 to 1100 ° C. for a period of 30 to 50 hours, preferably by bringing the temperature of the part to rise so that the gases are released. resulting from pyrolysis is progressive.
  • the inorganic powder is partially sintered and one thus obtains, following this treatment, a porous matrix containing a homogeneous dispersion of inclusions of vitreous carbon.
  • the product obtained following this second heat treatment is subjected to densification which can be carried out, optionally after grinding or deformation, by the conventional techniques of metallurgy of powders and / or by infiltration using a molten or gaseous compound.
  • This densification operation can be carried out for example by sintering under load, by hot isostatic compression, by hot spinning of powder contained in a tight sheath or by hot extrusion.
  • a composite material comprising inclusions of carbonaceous materials constituted at least in part by graphite
  • the first and second heat treatments are carried out as previously optionally after having subjected the mixture to a compression shaping operation, and the composite material comprising inclusions of vitreous carbon to an additional graphitization treatment by bringing it to a temperature at most equal to 2200 ° C.
  • the glassy carbon inclusions are transformed at least partially into graphite. In fact, this is obtained by adding graphite powder or boron nitride to the liquid resin because the vitreous carbon can only graphite with additives or external mechanical agents.
  • the inorganic powder used is a refractory powder that cannot be melted under the temperature conditions of the graphitization heat treatment.
  • the composite material comprising glassy carbon inclusions obtained following the second is subjected. heat treatment, to a complementary treatment in order to react at least in part the carbon of the inclusions with the matrix and thus form inclusions of carbide dispersed in this matrix.
  • This reaction can be carried out, for example, during a densification operation by hot isostatic compression, which also makes it possible to reduce the porosity possibly formed during the reaction.
  • the present invention also relates to a composite material obtained by this process, usable in particular for the production of electrical contacts.
  • the composite material is characterized in that it comprises a metallic inorganic matrix, preferably made of copper, in which inclusions of vitreous carbon are dispersed.
  • the glassy carbon inclusions represent at most 8% by weight of the composite material and they preferably have dimensions of less than 500 J.Lm.
  • Such a material can be used in particular to produce pairs of symmetrical electrical contacts intended to replace the contact pairs currently used such as silver-nickel and silver-copper contacts, in low and medium voltage electrical circuit breakers.
  • the composite materials of the invention containing approximately 3% by weight of vitreous carbon have satisfactory properties for this application: their contact resistance as well as their resistance to erosion remain acceptable during cycles of 5000 cuts of '' a nominal current of 100 amperes or after breaking of a short-circuit current of 1,500 to 13,000 amperes; in the case of closure with rebound the resistance to welding is also satisfactory even in the event of a short-circuit current being established; however, during a cycle of 1200 closings-openings without current, the contact resistance can reach a too high value if the size of the carbon inclusions exceeds 500 microns (the contact resistance increases during the first 100 operations approximately then reached a plateau).
  • composite materials with fine dispersion are preferably used, that is to say materials in which the size of the inclusions of vitreous carbon does not exceed 500 microns.
  • FIG. 1 is a diagram illustrating the change in temperature as a function of time during the second heat treatment used for the preparation of composite materials according to the invention.
  • FIGS. 2 and 3 are micrographs carried out respectively on a cross section and on a longitudinal section of the spun material obtained in example 3.
  • the composite material is manufactured in the following manner.
  • the density of the vitreous carbon included in the composite materials is 1.15 ⁇ 0.6.
  • composition of the material and the dimension of the inclusions can be adjusted independently of one another by acting respectively on the resin content and the particle size.
  • micrography carried out on the longitudinal metallographic section shows a tendency to align carbon inclusions in the spinning direction as well as veins or fibers of pure copper. It has been observed that the width of these veins increases with the particle size of the starting powder and that it decreases slightly when the vitreous carbon content increases.

Description

La présente invention se rapporte à des matériaux composites comportant une matrice inorganique dans laquelle sont réparties des inclusions de matériau carboné, constituées par des inclusions de carbone vitreux et/ou de graphite et/ou de carbures.The present invention relates to composite materials comprising an inorganic matrix in which are included inclusions of carbonaceous material, constituted by inclusions of vitreous carbon and / or graphite and / or carbides.

De tels matériaux composites peuvent être utilisés dans de nombreux domaines, en particulier dans l'industrie électrotechnique et mécanique en tant que matériaux de contact électrique et/ou matériaux de frottement.Such composite materials can be used in many fields, in particular in the electrical engineering and mechanical industry as electrical contact materials and / or friction materials.

De façon plus précise, l'invention concerne un procédé de préparation de matériaux composites comportant des inclusions de carbone vitreux de dimensions contrôlées, réparties d'une manière sensiblement uniforme et régulière au sein d'une matrice inorganique dense ou poreuse, de préférence métallique.More specifically, the invention relates to a process for preparing composite materials comprising vitreous carbon inclusions of controlled dimensions, distributed in a substantially uniform and regular manner within a dense or porous inorganic matrix, preferably metallic.

On rappelle que le carbone vitreux est une variété artificielle du carbone qui est obtenue par pyrolyse, dans des conditions rigoureusement contrôlées, de polymères réticulés obtenus par polycondensation de phénols et d'aldéhydes. Le carbone obtenu lors de cette pyrolyse est appelé carbone vitreux en raison de son aspect, de sa dureté, de sa fragilité (comparable à celle d'une porcelaine), et de son imperméabilité aux gaz qui sont comparables à ceux du verre.It is recalled that vitreous carbon is an artificial variety of carbon which is obtained by pyrolysis, under rigorously controlled conditions, of crosslinked polymers obtained by polycondensation of phenols and aldehydes. The carbon obtained during this pyrolysis is called vitreous carbon because of its appearance, its hardness, its brittleness (comparable to that of porcelain), and its impermeability to gases which are comparable to those of glass.

Pour obtenir ce carbone vitreux, la pyrolyse du polymère réticulé est conduite de telle sorte que le réseau tridimensionnel du polymère soit conservé pendant l'opération et confère au produit final cette structure particulière.To obtain this vitreous carbon, the pyrolysis of the crosslinked polymer is carried out in such a way that the three-dimensional network of the polymer is preserved during the operation and gives the final product this particular structure.

Le carbone vitreux présente des propriétés intéressantes pour diverses applications. En effet, compte tenu de sa structure particulière qui délimite des micropores ne communiquant pas entre eux et ne débouchant pas sur la surface du matériau, celui-ci présente une faible densité de l'ordre de 1,45 alors que celle du graphite est de 2,2. Par ailleurs, ses propriétés mécaniques sont voisines de celles du graphite pyrolithique ou du pyrocarbone ; et ses propriétés thermiques : une conductibilité thermique de l'ordre de 0,04 à 0,08 Joule/cm-1 · °C-1 · S-1 et un coefficient de dilatation de l'ordre de 3 à 5 · 106 · °C-1 à 100 °C et de 20 · 10-6 · °C-1 à 1 500 °C, lui confèrent une remarquable résistance aux chocs thermiques. De plus, le carbone vitreux présente une résistance à l'oxydation supérieure à celle des autres variétés de carbone et de graphite en particulier une bonne résistance à l'oxydation par l'oxygène, la vapeur d'eau ou le gaz carbonique.Vitreous carbon has interesting properties for various applications. Indeed, given its particular structure which delimits micropores which do not communicate with each other and do not open onto the surface of the material, the latter has a low density of the order of 1.45 whereas that of graphite is 2.2. Furthermore, its mechanical properties are close to those of pyrolithic graphite or pyrocarbon; and its thermal properties: a thermal conductivity of the order of 0.04 to 0.08 Joule / cm -1 · ° C -1 · S -1 and a coefficient of expansion of the order of 3 to 5 · 10 6 · ° C -1 to 100 ° C and from 20 · 10 -6 · ° C -1 to 1500 ° C, give it remarkable resistance to thermal shock. In addition, vitreous carbon has a higher resistance to oxidation than that of other varieties of carbon and graphite, in particular a good resistance to oxidation by oxygen, water vapor or carbon dioxide.

Aussi, on peut améliorer les propriétés mécaniques, thermiques, et/ou chimiques de certains matériaux inorganiques en leur ajoutant du carbone vitreux. Depuis quelques années, on a tenté de réaliser des matériaux composites comportant soit des inclusions de carbone vitreux, soit un revêtement de carbone vitreux. Cependant, les procédés utilisés jusqu'à présent n'ont pas permis d'obtenir un matériau composite comportant une matrice inorganique dans laquelle sont dispersées en proportion voulue des inclusions de carbone vitreux de dimensions contrôlées.Also, the mechanical, thermal, and / or chemical properties of certain inorganic materials can be improved by adding glassy carbon to them. In recent years, attempts have been made to make composite materials comprising either vitreous carbon inclusions or a vitreous carbon coating. However, the methods used until now have not made it possible to obtain a composite material comprising an inorganic matrix in which are dispersed in a desired proportion inclusions of vitreous carbon of controlled dimensions.

La présente invention a précisément pour objet un procédé de préparation d'un matériau composite comportant des inclusions de matériaux carbonés, en particulier de carbone vitreux, qui permet d'obtenir une dispersion uniforme et régulière de ces inclusions au sein d'une matrice inorganique poreuse ou compacte tout en contrôlant la dimension maximale de ces inclusions ainsi que la teneur en matériau carboné du produit obtenu.The present invention specifically relates to a process for preparing a composite material comprising inclusions of carbonaceous materials, in particular vitreous carbon, which makes it possible to obtain a uniform and regular dispersion of these inclusions within a porous inorganic matrix. or compact while controlling the maximum dimension of these inclusions as well as the content of carbonaceous material in the product obtained.

A cet effet, le procédé selon l'invention, de préparation d'un matériau composite comportant une matrice inorganique dans laquelle sont réparties des inclusions de matériau carboné, se caractérise en ce qu'il comprend les étapes suivantes :

  • a) mélanger une poudre inorganique frittable avec une résine liquide susceptible d'être transformée en carbone vitreux par traitement thermique,
  • b) soumettre le mélange de résine et de poudre inorganique à un premier traitement thermique effectué dans des conditions telles qu'on obtient un durcissement de la résine par réticulation ou polycondensation, et
  • c) soumettre le produit durci ainsi obtenu à un deuxième traitement thermique pour transformer la résine en carbone vitreux et former ainsi lesdites inclusions de carbone vitreux.
To this end, the process according to the invention, for preparing a composite material comprising an inorganic matrix in which inclusions of carbonaceous material are distributed, is characterized in that it comprises the following steps:
  • a) mixing a sinterable inorganic powder with a liquid resin capable of being transformed into vitreous carbon by heat treatment,
  • b) subjecting the mixture of resin and inorganic powder to a first heat treatment carried out under conditions such that hardening of the resin is obtained by crosslinking or polycondensation, and
  • c) subjecting the hardened product thus obtained to a second heat treatment to transform the resin into glassy carbon and thus form said inclusions of glassy carbon.

Le fait de partir d'un mélange comprenant la résine à l'état liquide et une poudre de matériau constituant la matrice, et de réaliser « in situ » les inclusions de carbone vitreux dans la masse du produit par traitement thermique du mélange permet non seulement d'obtenir une répartition homogène de ces inclusions mais également de contrôler d'une part, les dimensions en agissant sur la granulométrie de la poudre de départ et, d'autre part, la teneur en carbone vitreux du produit obtenu en agissant sur la teneur en résine du mélange.The fact of starting from a mixture comprising the resin in the liquid state and a powder of material constituting the matrix, and of carrying out “in situ” the inclusions of vitreous carbon in the mass of the product by heat treatment of the mixture allows not only to obtain a homogeneous distribution of these inclusions but also to control on the one hand, the dimensions by acting on the particle size of the starting powder and, on the other hand, the vitreous carbon content of the product obtained by acting on the content resin of the mixture.

En effet, on a trouvé que les dimensions des inclusions augmentaient avec la granulométrie de la poudre inorganique. Par ailleurs, on a vérifié que la teneur en carbone vitreux du produit augmente avec la teneur en résine du mélange de départ.Indeed, it has been found that the dimensions of the inclusions increase with the particle size of the inorganic powder. Furthermore, it has been verified that the vitreous carbon content of the product increases with the resin content of the starting mixture.

En revanche, on a trouvé que les dimensions des inclusions ne dépendaient que très peu de la teneur en résine du mélange de départ. Ainsi, le procédé de l'invention permet de réaliser efficacement et économiquement le contrôle de la composition du produit indépendamment du contrôle de la taille des inclusions.On the other hand, it has been found that the dimensions of the inclusions depend very little on the resin content of the starting mixture. Thus, the process of the invention makes it possible to carry out effectively and economically the control of the composition of the product independently of the control of the size of the inclusions.

Far ailleurs, en mélangeant une résine à l'état liquide avec une poudre inorganique de granulométrie contrôlée, on peut obtenir une pâte, homogène présentant une porosité ouverte, ce qui permet lors des deux traitements thermiques d'assurer l'évacuation des gaz libérés et de prévenir ainsi la formation d'une porosité importante et irrégulière et d'éviter également l'apparition de fissures.Far elsewhere, by mixing a resin in the liquid state with an inorganic powder of controlled particle size, it is possible to obtain a homogeneous paste having an open porosity, which makes it possible during the two heat treatments to ensure the evacuation of the gases released and thus preventing the formation of a large and irregular porosity and also avoiding the appearance of cracks.

Avantageusement, avant de réaliser le premier traitement thermique, on soumet le mélange de résine et de poudre inorganique à une opé:ration de mise en forme par compression à froid, afin d'obtenir une préforme.Advantageously, before carrying out the first heat treatment, the mixture of resin and inorganic powder is subjected to a shaping operation by cold compression, in order to obtain a preform.

Cette opération de compression peut être réalisée par pressage, filage, laminage ou extrusion de façon à mettre la pâte sous la forme de feuilles, de cylindres, etc.... mais elle est effectuée, de préférence, dans des conditions telles que la pâte ne devient pas compacte pour autoriser l'évacuation des gaz lors des traitements thermiques ultérieurs.This compression operation can be carried out by pressing, spinning, rolling or extruding so as to put the dough in the form of sheets, cylinders, etc., but it is preferably carried out under conditions such as the dough does not become compact to allow the evacuation of gases during subsequent heat treatments.

Toutefois, on peut réaliser les traitements thermiques sur une pâte compacte. Mais dans ce cas, il est nécessaire de soumettre le matériau obtenu à une opération complémentaire de densification éventuellement après broyage, pour éliminer la porosité.However, the heat treatments can be carried out on a compact paste. However, in this case, it is necessary to subject the material obtained to an additional densification operation, possibly after grinding, in order to eliminate the porosity.

Selon l'invention, la poudre inorganique utilisée est une poudre frittable, c'est-à-dire d'un matériau inorganique susceptible d'être mis en forme et consolidé par les techniques de la métallurgie des poudres ; par ailleurs, ce matériau inorganique est choisi de façon telle qu'il ne soit pas fusible aux températures utilisées pour les premier et deuxième traitements thermiques. A titre de matériaux inorganiques susceptibles d'être utilisés, on peut citer les métaux tels que le cuivre et le nickel; les alliages, lès céramiques telles que les oxydes, les carbures et les nitrures, par exempte le nitrure de bore, et les cermets. On peut aussi utiliser des poudres revêtues ou des mélanges de poudres de matériaux différents, par exemple, de matériaux susceptibles de réagir entre eux dans les conditions de traitement pour former une phase liquide.According to the invention, the inorganic powder used is a sinterable powder, that is to say of an inorganic material capable of being shaped and consolidated by the techniques of powder metallurgy; moreover, this inorganic material is chosen so that it is not fusible at the temperatures used for the first and second heat treatments. Mention may be made, as inorganic materials which can be used, of metals such as copper and nickel; alloys, ceramics such as oxides, carbides and nitrides, for example boron nitride, and cermets. It is also possible to use coated powders or mixtures of powders of different materials, for example, materials capable of reacting with each other under the processing conditions to form a liquid phase.

La granulométrie de la poudre inorganique utilisée est choisie en fonction de la dimension d'inclusions que l'on veut obtenir. Généralement, on utilise une poudre dont la granulométrie moyenne est comprise entre 0 et 600 µm.The particle size of the inorganic powder used is chosen according to the dimension of inclusions which it is desired to obtain. Generally, a powder is used whose average particle size is between 0 and 600 μm.

Selon l'invention, la résine utilisée est avantageusement une résine liquide, comportant des radicaux phénoliques (tels le phénol, le résorcinol, le naphtalène diol, etc...) et des radicaux dérivés d'aldéhydes (tels le formol, le glyoxal, le furfuraldéhyde, etc...).According to the invention, the resin used is advantageously a liquid resin, comprising phenolic radicals (such as phenol, resorcinol, naphthalene diol, etc.) and radicals derived from aldehydes (such as formaldehyde, glyoxal, furfuraldehyde, etc.).

De préférence, la résine liquide est une résine phénol formaldéhyde.Preferably, the liquid resin is a phenol formaldehyde resin.

Avantageusement, le mélange de résine et de poudre inorganique contient au plus 20 % en poids de résine.Advantageously, the mixture of resin and inorganic powder contains at most 20% by weight of resin.

Selon l'invention, le premier traitement thermique est avantageusement réalisé à une température au plus égale à 350 °C pendant une durée de 1 à 3 heures. Au cours de ce premier traitement thermique, on obtient la polycondensation de la résine, ce qui conduit à la formation d'un polymère réticulé solide et à l'obtention d'un produit durci. Grâce à la porosité de la pâte de départ, les gaz libérés lors de cette réaction peuvent être évacués, ce qui permet d'éviter l'apparition d'une porosité importante et/ou la formation de fissures dans le produit durci. Ce produit durci est ensuite soumis à un deuxième traitement thermique pour transformer le polymère solide en carbone vitreux. Ce deuxième traitement doit être effectué dans des conditions rigoureusement contrôlées de façon à conserver le réseau tridimensionnel du polymère solide réticulé.According to the invention, the first heat treatment is advantageously carried out at a temperature at most equal to 350 ° C. for a period of 1 to 3 hours. During this first heat treatment, polycondensation of the resin is obtained, which leads to the formation of a solid crosslinked polymer and to the obtaining of a cured product. Thanks to the porosity of the starting paste, the gases released during this reaction can be evacuated, which makes it possible to avoid the appearance of significant porosity and / or the formation of cracks in the cured product. This hardened product is then subjected to a second heat treatment to transform the solid polymer into vitreous carbon. This second treatment must be carried out under rigorously controlled conditions so as to preserve the three-dimensional network of the crosslinked solid polymer.

Ainsi, lors de la réalisation de ce traitement thermique, il est nécessaire de contrôler notamment la vitesse de montée en température, ainsi que la température et la durée du traitement. Avantageusement, on réalise ce deuxième traitement sous vide ou sous atmosphère neutre à une température de 600 à 1 100 °C pendant une durée de 30 à 50 heures en réalisant de préférence la montée en température de la pièce de façon telle que la libération des gaz résultant de la pyrolyse soit progressive.Thus, when carrying out this heat treatment, it is necessary to control in particular the rate of temperature rise, as well as the temperature and the duration of the treatment. Advantageously, this second treatment is carried out under vacuum or under a neutral atmosphere at a temperature of 600 to 1100 ° C. for a period of 30 to 50 hours, preferably by bringing the temperature of the part to rise so that the gases are released. resulting from pyrolysis is progressive.

Au cours de ce traitement, la poudre inorganique est partiellement frittée et l'on obtient ainsi, à la suite de ce traitement, une matrice poreuse contenant une dispersion homogène d'inclusions de carbone vitreux.During this treatment, the inorganic powder is partially sintered and one thus obtains, following this treatment, a porous matrix containing a homogeneous dispersion of inclusions of vitreous carbon.

Lorsqu'on veut obtenir un matériau composite dans lequel la matrice est dense, on soumet le produit obtenu à la suite de ce deuxième traitement thermique à une densification qui peut être réalisée, éventuellement après broyage ou déformation, par les techniques classiques de la métallurgie des poudres et/ou par infiltration au moyen d'un composé fondu ou gazeux.When it is desired to obtain a composite material in which the matrix is dense, the product obtained following this second heat treatment is subjected to densification which can be carried out, optionally after grinding or deformation, by the conventional techniques of metallurgy of powders and / or by infiltration using a molten or gaseous compound.

Cette opération de densification peut être réalisée par exemple par frittage sous charge, par compression isostatique à chaud, par filage à chaud de poudre contenue dans une gaine étanche ou par extrusion à chaud.This densification operation can be carried out for example by sintering under load, by hot isostatic compression, by hot spinning of powder contained in a tight sheath or by hot extrusion.

Selon une variante de mise en oeuvre du procédé de l'invention, adaptée à la fabrication d'un matériau composite comportant des inclusions de matériaux carbonés constitués au moins en partie par du graphite, on part d'un mélange de poudre inorganique et de résine liquide à laquelle on a ajouté de la poudre fine de graphite ou de nitrure de bore, puis on réalise le premier et le deuxième traitements thermiques comme précédemment éventuellement après avoir soumis le mélange à une opération de mise en forme par compression, et on soumet le matériau composite comportant des inclusions de carbone vitreux à un traitement complémentaire de graphitisation en le portant à une température au plus égale à 2 200 °C. Dans ces conditions, les inclusions de carbone vitreux se transforment au moins partiellement en graphite. En effet, ceci est obtenu grâce à l'adjonction de poudre de graphite ou de nitrure de bore à la résine liquide car le carbone vitreux ne peut se graphiter qu'avec des additifs ou des agents mécaniques extérieurs.According to an alternative implementation of the method of the invention, suitable for the manufacture of a composite material comprising inclusions of carbonaceous materials constituted at least in part by graphite, one starts with a mixture of inorganic powder and resin liquid to which fine graphite or boron nitride powder has been added, then the first and second heat treatments are carried out as previously optionally after having subjected the mixture to a compression shaping operation, and the composite material comprising inclusions of vitreous carbon to an additional graphitization treatment by bringing it to a temperature at most equal to 2200 ° C. Under these conditions, the glassy carbon inclusions are transformed at least partially into graphite. In fact, this is obtained by adding graphite powder or boron nitride to the liquid resin because the vitreous carbon can only graphite with additives or external mechanical agents.

Dans cette variante, la poudre inorganique utilisée est une poudre réfractaire non fusible dans les conditions de température du traitement thermique de graphitisation.In this variant, the inorganic powder used is a refractory powder that cannot be melted under the temperature conditions of the graphitization heat treatment.

Selon une seconde variante de mise en oeuvre du procédé de l'invention, particulièrement adaptée à la fabrication de matériaux composites dont les inclusions sont en partie constituées de carbure, on soumet le matériau composite comportant des inclusions de carbone vitreux obtenu à la suite du second traitement thermique, à un traitement complémentaire afin de faire réagir au moins en partie le carbone des inclusions avec la matrice et former ainsi des inclusions de carbure dispersées dans cette matrice. Cette réaction peut être réalisée, par exemple, au cours d'une opération de densification par compression isostatique à chaud, ce qui permet de plus de réduire la porosité éventuellement formée lors de la réaction.According to a second variant of implementation of the method of the invention, particularly suitable for the manufacture of composite materials, the inclusions of which are partly made of carbide, the composite material comprising glassy carbon inclusions obtained following the second is subjected. heat treatment, to a complementary treatment in order to react at least in part the carbon of the inclusions with the matrix and thus form inclusions of carbide dispersed in this matrix. This reaction can be carried out, for example, during a densification operation by hot isostatic compression, which also makes it possible to reduce the porosity possibly formed during the reaction.

La présente invention a également pour objet un matériau composite obtenu par ce procédé, utilisable notamment pour la réalisation de contacts électriques.The present invention also relates to a composite material obtained by this process, usable in particular for the production of electrical contacts.

Pour cette utilisation, le matériau composite se caractérise en ce qu'il comprend une matrice inorganique métallique, de préférence en cuivre, dans laquelle sont dispersées des inclusions de carbone vitreux. Dans ce cas, les inclusions de carbone vitreux représentent au plus 8 % en poids du matériau composite et elles ont de préférence des dimensions inférieures à 500 J.Lm.For this use, the composite material is characterized in that it comprises a metallic inorganic matrix, preferably made of copper, in which inclusions of vitreous carbon are dispersed. In this case, the glassy carbon inclusions represent at most 8% by weight of the composite material and they preferably have dimensions of less than 500 J.Lm.

Un tel matériau peut être utilisé en particulier pour réaliser des paires de contacts électriques symétriques destinées à remplacer les paires de contact utilisées actuellement telles que les contacts argent-nickel et argent-cuivre, dans les disjoncteurs électriques basse et moyenne tensions. En effet, les matériaux composites de l'invention contenant environ 3 % en poids de carbone vitreux présentent des propriétés satisfaisantes pour cette application : leur résistance de contact ainsi que leur résistance à l'érosion restent acceptables au cours de cycles de 5 000 coupures d'un courant nominal de 100 ampères ou après coupures d'un courant de court-circuit de 1 500 à 13000 ampères ; dans le cas de fermeture avec rebond la résistance à la soudure est également satisfaisante même en cas d'établissement d'un courant de court-circuit ; cependant, au cours d'un cycle de 1 200 fermetures-ouvertures sans courant, la résistance de contact peut atteindre une valeur trop élevée si la taille des inclusions de carbone dépasse 500 microns (la résistance de contact croît pendant les 100 premières manoeuvres environ puis atteint un palier).Such a material can be used in particular to produce pairs of symmetrical electrical contacts intended to replace the contact pairs currently used such as silver-nickel and silver-copper contacts, in low and medium voltage electrical circuit breakers. Indeed, the composite materials of the invention containing approximately 3% by weight of vitreous carbon have satisfactory properties for this application: their contact resistance as well as their resistance to erosion remain acceptable during cycles of 5000 cuts of '' a nominal current of 100 amperes or after breaking of a short-circuit current of 1,500 to 13,000 amperes; in the case of closure with rebound the resistance to welding is also satisfactory even in the event of a short-circuit current being established; however, during a cycle of 1200 closings-openings without current, the contact resistance can reach a too high value if the size of the carbon inclusions exceeds 500 microns (the contact resistance increases during the first 100 operations approximately then reached a plateau).

Aussi, on utilise de préférence des matériaux composites à dispersion fine, c'est-à-dire des matériaux dans lesquels la taille des inclusions de carbone vitreux ne dépasse pas 500 microns.Also, composite materials with fine dispersion are preferably used, that is to say materials in which the size of the inclusions of vitreous carbon does not exceed 500 microns.

En revanche, lorsqu'on utilise des contacts composites cuivre-graphite dans les mêmes conditions, il se produit une augmentation inacceptable de la résistance de contact au cours d'un cycle de 5000 coupures d'un courant nominal de 100 ampères, cette différence de comportement est probablement liée à la plus faible réactivité du carbone vitreux vis-à-vis de l'oxygène.On the other hand, when copper-graphite composite contacts are used under the same conditions, an unacceptable increase in the contact resistance occurs during a cycle of 5000 cuts of a nominal current of 100 amperes, this difference of behavior is probably linked to the lower reactivity of vitreous carbon towards oxygen.

D'autres avantages et caractéristiques de l'invention apparaîtront mieux à la lecture des exemples suivants, donnés bien entendu à titre illustratif et non limitatif, en référence au dessin annexé sur lequel :Other advantages and characteristics of the invention will appear more clearly on reading the following examples, given of course by way of illustration and not limitation, with reference to the appended drawing in which:

la figure 1 est un diagramme illustrant l'évolution de la température en fonction du temps lors du deuxième traitement thermique mis en oeuvre pour la préparation de matériaux composites selon l'invention, etFIG. 1 is a diagram illustrating the change in temperature as a function of time during the second heat treatment used for the preparation of composite materials according to the invention, and

les figures 2 et 3 sont des micrographies effectuées respectivement sur une coupe transversale et sur une coupe longitudinale du matériau filé obtenu dans l'exemple 3.FIGS. 2 and 3 are micrographs carried out respectively on a cross section and on a longitudinal section of the spun material obtained in example 3.

Ces exemples se rapportent à la préparation de matériaux composites comportant une matrice de cuivre et des inclusions de carbone vitreux, de tels matériaux pouvant être utilisés en particulier comme contacts électriques dans les disjoncteurs basse et moyenne tensions.These examples relate to the preparation of composite materials comprising a copper matrix and vitreous carbon inclusions, such materials being able to be used in particular as electrical contacts in low and medium voltage circuit breakers.

Dans ces exemples, on fait seulement varier les teneurs en résine du mélange de départ et la granulométrie de la poudre de cuivre utilisée. Dans chaque exemple, le matériau composite est fabriqué de la façon suivante.In these examples, only the resin contents of the starting mixture and the particle size of the copper powder used are varied. In each example, the composite material is manufactured in the following manner.

On prépare une pâte par mélange mécanique de poudre de cuivre et de résine phénol-formaldéhyde, puis on pastille la pâte en galettes de 70 g environ et on soumet les galettes obtenues à un premier traitement thermique réalisé à 120 °C à l'air pendant 2 heures et à un deuxième traitement thermique effectué sous vide dans les conditions de durée et de température représentés par le cycle de la figure 1 qui est un diagramme représentant l'évolution de la température (°C) en fonction du temps (en heures) pendant ce traitement thermique ; on conditionne ensuite sous vide les galettes poreuses de cuivre- carbone vitreux ainsi obtenues, dans des gaines de filage en cuivre et on réalise le filage sous gaine dans les conditions suivantes :

  • - température de préchauffage : 860 °C,
  • - rapport de filage : = 20,
  • - pression de filage : 604 bars,
  • - vitesse de sortie : 50 m/min.,
  • - diamètre des pots de filage : 43,5 mm, sauf dans le cas de l'exemple 5 où il est de 91,5 mm,
  • - diamètre de filière : 10 mm, sauf dans le cas de l'exemple 5 où il est de 22 mm.
A dough is prepared by mechanical mixing of copper powder and phenol-formaldehyde resin, then the dough is pelleted in cakes of approximately 70 g and the cakes obtained are subjected to a first heat treatment carried out at 120 ° C. in air for 2 hours and a second heat treatment carried out under vacuum under the conditions of duration and temperature represented by the cycle of FIG. 1 which is a diagram representing the evolution of the temperature (° C) as a function of time (in hours) during this heat treatment; the porous wafers of vitreous copper-carbon thus obtained are then vacuum-conditioned in copper spinning sheaths and the sheath spinning is carried out under the following conditions:
  • - preheating temperature: 860 ° C,
  • - spinning ratio: = 20,
  • - spinning pressure: 604 bars,
  • - exit speed: 50 m / min.,
  • - diameter of the spinning pots: 43.5 mm, except in the case of Example 5 where it is 91.5 mm,
  • - die diameter: 10 mm, except in the case of Example 5 where it is 22 mm.

On obtient ainsi différents matériaux composites présentant les propriétés données dans le tableau qui suit. Dans ce tableau, on a également indiqué pour chaque exemple la granulométrie de la poudre de cuivre et le rapport en poids masse de résine/masse de poudre de cuivre utilisés.Various composite materials are thus obtained having the properties given in the table below. In this table, the particle size of the copper powder and the weight ratio of resin mass / mass of copper powder used are also indicated for each example.

(Voir Tableau page suivante)(See Table on next page)

Figure imgb0001
Au vu de ces résultats, on constate que :

  • - la teneur en carbone vitreux des matériaux composites, déterminée par analyse chimique et exprimée en pourcentage par rapport au poids total du matériau composite, est proportionnelle à la masse de résine présente dans le mélange de départ,
  • - les dimensions des inclusions augmentent avec la granulométrie de la poudre de cuivre en étant pratiquement indépendantes de la teneur globale en carbone ; et
  • - la densité des matériaux composites diminue rapidement en fonction de leur teneur en carbone vitreux.
Figure imgb0001
 In view of these results, we note that:
  • the vitreous carbon content of the composite materials, determined by chemical analysis and expressed as a percentage relative to the total weight of the composite material, is proportional to the mass of resin present in the starting mixture,
  • - The dimensions of the inclusions increase with the particle size of the copper powder while being practically independent of the overall carbon content; and
  • - the density of composite materials decreases rapidly depending on their vitreous carbon content.

En comparant ces résultats expérimentaux à des courbes théoriques, on peut estimer que la densité du carbone vitreux inclus dans les matériaux composites est de 1,15 ±0,6.By comparing these experimental results to theoretical curves, it can be estimated that the density of the vitreous carbon included in the composite materials is 1.15 ± 0.6.

Ainsi, ces résultats confirment qu'on peut régler la composition du matériau et la dimension des inclusions indépendamment l'une de l'autre en agissant respectivement sur la teneur en résine et la granulométrie.Thus, these results confirm that the composition of the material and the dimension of the inclusions can be adjusted independently of one another by acting respectively on the resin content and the particle size.

En se reportant maintenant aux figures 2 et 3 qui sont des micrographies effectuées respectivement sur une coupe transversale et sur une coupe longitudinale du matériau composite obtenu dans l'exemple 3, on constate que le matériau obtenu présente une excellente homogénéité.Referring now to Figures 2 and 3 which are micrographs performed respectively on a cross section and a longitudinal section of the composite material obtained in Example 3, it is found that the material obtained has excellent homogeneity.

Par ailleurs, la micrographie effectuée sur la coupe métallographique longitudinale montre une tendance à l'alignement des inclusions de carbone dans la direction de filage ainsi que des veines ou fibres de cuivre pur. On a pu constater que la largeur de ces veines croît avec la granulométrie de la poudre de départ et qu'elle décroît légèrement quand la teneur en carbone vitreux augmente.In addition, the micrography carried out on the longitudinal metallographic section shows a tendency to align carbon inclusions in the spinning direction as well as veins or fibers of pure copper. It has been observed that the width of these veins increases with the particle size of the starting powder and that it decreases slightly when the vitreous carbon content increases.

Claims (16)

1. Process for the preparation of a composite material comprising an inorganic matrix, in which are distributed inclusions of carbonaceous material, characterized in that it comprises the following stages :
a) mixing a sinterable inorganic powder with a liquid resin capable of being transformed into vitreous carbon by heat treatment,
b) subjecting the mixture of resin and inorganic powder to a first heat treatment carried out under conditions such as to bring about hardening of the resin by crosslinking or polycondensation, and
c) subjecting the thereby-obtained hardened product to a second heat treatment to convert the resin into vitreous carbon and thereby to form the said inclusions of vitreous carbon.
2. Process according to Claim 1, characterized in that before carrying out the first heat treatment, the mixture of resin and powder is moulded by cold compression to form a green blank.
3. Process according to either of Claims 1 and 2, characterized in that the inorganic powder is a metal or alloy powder.
4. Process according to Claim 3 characterized in that the inorganic powder is copper powder.
5. Process according to any one of Claims 1 to 4, characterized in that the resin is a resin having phenol groups and groups derived from aldehydes.
6. Process according to Claim 5, characterized in that the resin is a phenol-formaldehyde resin.
7. Process according to any one of Claims 1 to 6, characterized in that the mixture of resin and inorganic powder contains at most 20 % by weight of resin.
8. Process according to any one of Claims 1 to 7, characterized in that the first heat treatment is carried out at a temperature of at most 350 °C for a period of 1 to 3 hours.
9. Process according to any one of Claims 1 to 8, characterized in that the second heat treatment is carried out under vacuum, or in an inert atmosphere, at a temperature of 600 to 1100 °C for a period of 30 to 50 hours.
10. Process according to any one of Claims 1 to 9, characterized in that the composite material comprising inclusions of vitreous carbon, obtained at the end of the second heat treatment, is subjected to a densification treatment.
11. Process according to Claim 10, characterized in that the densification is achieved by spinning when hot, and/or by isostatic compression when hot.
12. Process according to any one of Claims 1 to 9, characterized in that the liquid resin employed in step (a) contains graphite powder and/or boron nitride powder, and in that the composite material comprising vitreous carbon inclusions obtained at the end of the second heat treatment is subjected to a further heat treatment for graphitisation, carried out at a temperature of at most 2 200 °C to convert at least a part of the vitreous carbon inclusions into graphite, the inorganic powder being a refractory powder which is non-fusible under the temperature conditions of the graphitising heat treatment.
13. Process according to any one of Claims 1 to 9, characterized in that the composite material obtained at the end of the second heat treatment is subjected to a further treatment whereby to cause at least a part of the carbon in the inclusions to react with the inorganic matrix and thereby to form inclusions of carbide dispersed in said matrix.
14. Composite material obtained by a process according to any one of Claims 1 to 11, characterized in that it comprises a matrix of copper, within which are uniformly and homogeneously dispersed inclusions of vitreous carbon, the vitreous carbon content of said composite material being at most 8 % by weight.
15. Material according to Claim 14, characterized in that said inclusions have dimensions less than 500 RM.
16. Use of a composite material according to either of Claims 14 and 15 for the production of electrical contacts.
EP82401443A 1981-08-06 1982-07-30 Method of preparing a composite material comprising an inorganic matrix in which vitreous carbon inclusions are dispersed, material obtained by this process and its utilisation as an electric contact Expired EP0072306B1 (en)

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FR8115275 1981-08-06
FR8115275A FR2511040B1 (en) 1981-08-06 1981-08-06 PROCESS FOR THE PREPARATION OF A COMPOSITE MATERIAL COMPRISING AN INORGANIC MATRIX IN WHICH THE INCLUSIONS OF VITREOUS CARBON ARE DISTRIBUTED, MATERIAL OBTAINED BY THIS PROCESS AND ITS USE AS AN ELECTRIC CONTACT

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US4808354A (en) * 1987-06-22 1989-02-28 International Fuel Cells Corporation Method of making electrical discharge machining electrodes
US4810289A (en) * 1988-04-04 1989-03-07 Westinghouse Electric Corp. Hot isostatic pressing of high performance electrical components
DE19714561C1 (en) 1997-04-09 1998-10-22 Preh Elektro Feinmechanik Process for the production of powdery, glassy carbon, resistance paste with this carbon and use of this resistance paste as a resistance layer
AUPP773998A0 (en) * 1998-12-16 1999-01-21 Public Transport Corporation of Victoria Low resistivity materials with improved wear performance for electrical current transfer and methods for preparing same
FR3066418B1 (en) * 2017-05-18 2021-09-24 Commissariat Energie Atomique PROCESS FOR PREPARING A COMPOSITE MATERIAL WITH A METAL MATRIX BY INJECTION MOLDING
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